Archaeology on an Interstellar Scale

by Paul Gilster on April 16, 2013

Dyson spheres — technology wrapped around an entire star to maximize energy use — would be unimaginably big. But the idea of maximizing the light from a central star certainly makes sense. Imagine a sphere with a radius at the distance of Earth’s orbit. Now you’ve got a surface area more than 100 million times what’s available on our planet, a sensational venue for science fiction if nothing else. And you’re certainly changing the energy equation — our total power consumption today is the equivalent of about 0.01 percent of the sunlight falling on Earth, according to a new article in New Scientist. Keep energy demand growing at 1 percent per year and in a single millennium we’ll need more energy than strikes the surface of the planet.

Moving power generation into space is certainly something that would motivate a civilization a good deal more advanced than our own, and using abundant asteroid material, it could spread power generation entirely around the star. Stephen Battersby, who wrote Alien Megaprojects: The Hunt Has Begun, doubts they would create a single shell because it would be gravitationally unstable. But a Dyson ‘swarm’ is more plausible, with hordes of large power stations moving on independent orbits around the star. Dyson, who likes to talk about what is observable rather than what’s probable, thinks we could spot such a project through its waste heat in the infrared.

This wouldn’t be an easy catch because there are astronomical configurations — a young star in an envelope of gas and dust, for example — that radiate in the infrared in much the same way. But this, says Battersby, can be resolved:

…the infrared spectrum of these objects should be a giveaway. Silicate minerals in dust produce a distinctive broad peak in the spectrum, and molecules in a warm gas would produce bright or dark spectral lines at specific wavelengths. By contrast, waste heat from a sphere should have a smooth, featureless thermal spectrum. “We would be hoping that the spectrum looks boring,” says Matt Povich at the California State Polytechnic University in Pomona. “The more boring the better.”

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Image: A mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release. Since the Infrared Astronomical Satellite mission of 1983, we have added greatly to our databases of infrared objects. Will new searches help us locate a source with a clearly artificial signature? Image credit: NASA/JPL-Caltech/UCLA.

And that brings us to Vyacheslav Ivanovich Slysh, a Russian radio astronomer known for the so-called ‘Slysh formula,’ which helps determine the size of sources of synchrotron radiation, an important contribution to the study of active galactic nuclei. Known as well for his work on maser emission in star-forming regions, Slysh turned his attention in 1985 to a survey of infrared data in the hunt for Dyson objects, whether spheres or swarms. Battersby mentions Slysh only in passing, but the Russian work on what I usually refer to as ‘interstellar archaeology’ in these pages is quite interesting. In 2000, Slysh’s work was followed by M. Y. Timofeev, collaborating with Nikolai Kardashev, both efforts using data from the Infrared Astronomical Satellite.

Centauri Dreams readers will know to associate the search for extraterrestrial artifacts with Richard Carrigan, a scientist emeritus in the Accelerator Division at the Fermi National Accel­era­tor Laboratory whose most recent search dates from 2009. Here’s what Carrigan says about the Slysh and Timofeev efforts in his Dyson Sphere Search History. Here he has just referred to a search by Jun Jugaku and Shiro Nishimura, looking for ‘partial’ Dyson spheres:

Slysh and Timofeev at al. have used the IRAS database for a different approach. Slysh investigates the flux at the maximum of a Dyson Sphere spectrum. He estimates that all Dyson Spheres with temperatures from 50 to 400 ºK within 1 kpc of the sun should have been detected. The Timofeev search looked at a population of IRAS sources in the 110-120 and 280-290 ºK temperature range as established by Kardashev and others and did Planck blackbody fits to the four IRAS bands. They fitted by minimizing to a Planck distribution. (Note that no Planck spectrum correction is made on the four measured fluxes from the filters.) Slysh identified one possible Dyson Sphere candidate, G357.3-1.3. The Timofeev at al. search identified 10 or so candidates but ruled out most of them, often on the basis of associations.

carrigan

That figure of 1 kiloparsec (kpc) from the Sun identified with Slysh is chosen for a reason. In 1966, Carl Sagan and Russell Walker published a paper in The Astrophysical Journal on “The Infrared Detectability of Dyson Civilizations.” Their analysis showed that a search out to 1000 parsecs should be possible even with the technology of the day, but noted the problem of confusing a possible Dyson signature with natural phenomena. Carrigan’s 2009 search also used the IRAS data of 250,000 infrared sources (it covers 96 percent of the sky), looking for both full and partial Dyson spheres in the blackbody temperature region from 100 K to 600 K. Carrigan’s limits don’t go out as far. He says that IRAS’ Low Resolution Spectrometer was sensitive enough to find Dyson spheres out to 300 parsecs. That would encompass roughly a million solar-type stars.

Image: Richard Carrigan, who told New Scientist for its recent article: “I wanted to get into the mode of the British Museum, to go and look for artifacts.”

I’ve mentioned enough papers to begin a small bibliography, which I’ll list here, but go to Carrigan’s site for other references. I bring all this up for two reasons. First, new searches for extraterrestrial artifacts are in the works, about which more tomorrow. The other reason is that this work isn’t highly visible, but the change it represents from more conventional radio and optical SETI methods is profound. The change speaks not so much to the failure of earlier SETI to produce a result as to our growing understanding that civilizations substantially more advanced than our own — if they exist — could work with engineering on mind-boggling scales. Such engineering should be detectable, and we’ll look at new efforts to find it tomorrow.

The Slysh paper is “A Search in the Infrared to Microwave for Astroengineering Activity,” in The Search for Extraterrestrial Life: Recent Developments, M. D. Papagiannis (Editor), Reidel Pub. Co., Boston, Massachusetts, 1985, p. 315. Timofeev and Kardashev wrote “A Search of the IRAS Database for Evidence of Dyson Spheres,” Acta Astronautica 46 (2000), p. 655. The Sagan and Walker paper is “The Infrared Delectability of Dyson Civilizations,” Astrophysical Journal 144 (3), (1966), p. 1216. And Richard Carrigan’s 2009 study is “The IRAS-based Whole-Sky Upper Limit on Dyson Spheres,” Astrophysical Journal 698 (2009), pp. 2075-2086, available online.

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FrankH April 16, 2013 at 15:07

I don’t think Dyson sphere’s make much sense for a civilization made up of independent meat units. An AI culture, sure.

What would be a more reasonable venture for critters like us is a Culture Orbital. It would provide a VAST habitable land surface. The exterior surface can work as both a collector (when it’s pointing at the star) and a radiator, and it should be visible in transits and maybe in the IR.

andy April 16, 2013 at 15:49

IIRC Culture Orbitals require tensile strength substantially higher than any known material. Not as severe as the Ringworld but still not a particularly feasible prospect.

As for Dyson spheres I am yet to be convinced about their long-term stability: avoiding collisions between the constituent satellites, Kessler syndrome, etc. (Though destruction of a Dyson sphere by Kessler syndrome would probably boost detectability by producing lots of dust…) Nice theoretical idea, but probably not all that practical.

As an aside, I personally find the viewpoint that sees all planets/celestial bodies/etc. as just things to be broken up for resources as a rather depressing one… and I wonder whether a culture with such a sense of aesthetics would really be worth the effort of contacting.

GaryChurch April 16, 2013 at 18:42

I cannot recall which one but one classic sci-fi novel was about the detection of a starship drive signature way out there and from that data we built our own ships and headed for the stars.

Since the only real star drive (capable of time dilation) proposed so far that does not require unobtanium is the small black hole engine and it does require gargantuan solar energy stations to manufacture, I believe this partial Dyson sphere search has merit.

Andrew W April 16, 2013 at 20:57

Any civilization capable of building these systems would have the resources to conquer the galaxy.

Where is everyone?

A. A. Jackson April 17, 2013 at 0:20

Here is ol broken record again, at least I am good company, Philip Morrison rejected these Malthusian Dyson and Kardashev objects mainly because he felt they were created out of ‘pure thought’ with no supporting empirical evidence.

For me it is modern evolutionary biology. It was the biologist Robert May who pointed exponential growth was too simple a model for evolutionary biology. The Logistic Map should be an important component, Martin Nowak expanded on this later on.
I don’t know how much this has been applied in Sociobiology but my guess is the true theories of civilization are non-linear and hence incorporating chaos, generating a horizon of predictability.
So, just flatly, we can’t even predict what we will be like as a complex technological civilization. (If we get there!)

mike shupp April 17, 2013 at 0:38

Gary Church:

STARFARERS, by Poul Anderson, published 1998.

Or so I’d guess. Decent tale, but profoundly melancholy.

A. A. Jackson April 17, 2013 at 12:25

@mike shupp
Paul is going to be disappointed in me on this one.
But I am sure that someone, could have been Anderson, long long before 1998 wrote stories when when an FTL ship jumped back from hyperspace to space, there was the equivalent of Cherenkov radiation.
I almost remember wrote one time that Asimov wished he had thought of that for his ‘jump drives’ used back in the 1940′s!
Even Babylon Five and maybe Star Trek used a version of it, but it existed in the prose form way way before those TV shows.

Paul Gilster April 17, 2013 at 13:47

Hey Al, you’ve never disappointed me yet! And I’ll admit that I can’t come up with the reference myself, though you’re right that this theme showed up way back in the day. I have to do some digging, but I’m thinking Analog back in the late Campbell era, maybe late 1960s? Will now obsess about this until I figure out the answer.

Dmitri April 17, 2013 at 16:00

Looking for signs of ETI? Look for the exploded two stars from Idiran War. If we already have ventured into the Culture civilizatsion and realm. Two stars in each other proximity exploding simultaneously is a too low probability to happen naturally. Most likely it’s the sign of the past war ;)

Wojciech J April 17, 2013 at 18:49

Excellent ! Finally a more reasonable SETI attempts(btw I do recall Paul writing about Dyson spheres much earlier). While the Dyson Spheres might not be the most likely outcome of our or other civilization, I guess possibility of one existing shouldn’t be excluded. With better instruments we could search for star-drives, night lights on exoplanets, asteroid mining, star mining and other mega-engineering projects.
For several reasons it makes more sense then search for radio waves(a fact that some of these objects can remain even when its creators have vanished is a good argument).

NS April 17, 2013 at 19:20

Don’t recall where I heard of this (probably here!) but it describes a data search for ETs using antimatter:

http://arxiv.org/abs/astro-ph/0112490

GaryChurch April 19, 2013 at 2:48

“-long long before 1998 wrote stories when an FTL ship jumped back from hyperspace to space, there was the equivalent of Cherenkov radiation.”

Well, there was no FTL in Starfarers- just extreme time dilation. It was fairly hard sci-fi except for the zero-zero-energy-from-nothing which I consider pretty soft.

All this skepticism about about other star travelers reminds me of the same kind of doubts concerning exoplanets- until they discovered them. If intelligent life is “rare” we have to qualify rare. With billions of galaxies it may be a case of our galaxy being one of those with an intelligent species; us. That does not mean there are not millions of other species spread across the universe. If star travel has a speed limitation in the low percentages of C as well as the maximum speed limit up there in high numbers, seeing evidence of travel or alien civilization may be problematic.

That should not stop us from going though. It is actually good news if rarity is the case- we may not have to worry much about cook books on how to prepare man.

At least some people consider humans intelligent- I have my doubts.

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